Method for producing skin-covered polyolefin resin foamed molded article

1. A method for producing a skin-covered polyolefin-based resin foamed molded article, comprising the steps of:

extruding a melt comprising a polyolefin-based resin to form a parison in a softened state;

blow-molding the parison into a skin defining a hollow interior space;

filling multi-layered expanded beads comprising a polyolefin-based resin in the hollow interior space;

forming holes for introducing steam into the hollow interior space through steam pins by inserting steam pins through the skin; and

heating the multi-layered expanded beads filled in the hollow interior space to fuse-bond the multi-layered expanded beads to each other and to fuse-bond the multi-layered expanded beads to the skin by introducing steam into the hollow interior space through the steam pins inserted through the holes,

wherein the multi-layered expanded beads fulfill the following requirements (a) to (e):

(a) the multi-layered expanded beads have an apparent density of 0.03 to 0.2 g/cm 3 ;

(b) the multi-layered expanded beads have an average diameter of 1.5 to 3.0 mm and are formed by expanding multi-layer resin particles each having a weight of 0.2 to 0.7 mg;

(c) the multi-layered expanded beads, when measured by heat-flux differential scanning calorimetry in which a sample thereof is heated from 23° C. to 220° C. at a heating rate of 10° C/min, gives a DSC curve which has an endothermic peak A intrinsic to the polyolefin-based resin of the multi-layered expanded beads and at least one endothermic peak B on a high temperature side of the endothermic peak A, and in which a ratio of the heat of fusion of the endothermic peak B to the total heat of fusion of the endothermic peaks is 0.15:1 to 0.25:1 and the endothermic peak B of the multi-layered expanded beads has a heat of fusion of 15 to 24 J/g;

(d) the multi-layered expanded beads have a surface layer having a melting point lower than that of a region inside the surface layer; and

(e) the polyolefin-based resin of which the multi-layered expanded beads are comprised is a polypropylene-based resin.

2. The method for producing a skin-covered polyolefin-based resin foamed molded article according to claim 1 ,

wherein each of the multi-layered expanded beads has an expanded core layer that is covered with the surface layer,

wherein the expanded core layer comprises a first polyolefin-based resin having a melting point Tc and the surface layer comprises a second polyolefin-based resin having a melting point Ts, and

wherein the melting points Tc and Ts satisfy the following relationship (1):

Tc (° C.) > Ts (° C.)  (1).

3. The method for producing a skin-covered polyolefin-based resin foamed molded article according to claim 2 , wherein the melting points Tc and Ts satisfy the following relationship (2):

Tc (° C.) − Ts (° C.) >3 (° C.)  (2).

4. The method for producing a skin-covered polyolefin-based resin foamed molded article according to claim 2 , wherein the multi-layered expanded beads are obtained by expanding multi-layer resin particles each of which has a core layer comprising the first polyolefin-based resin and an outer layer comprising the second polyolefin-based resin and wherein a weight ratio of the first polyolefin-based resin to the second polyolefin-based resin is 99.5:0.5 to 80:20.

5. The method for producing a skin-covered polyolefin-based resin foamed molded article according to claim 2 , wherein the polyolefin-based resin of which the expanded core layer is constituted is a polypropylene-based resin having a bending elastic modulus of 700 MPa or higher.

6. The method for producing a skin-covered polyolefin-based resin foamed molded article according to claim 1 , wherein the polyolefin-based resin of which the skin is constituted is a polypropylene-based resin having a melt tension at 230° C. of 1 to 30 cN.

7. The method for producing a skin-covered polyolefin-based resin foamed molded article according to claim 1 , wherein the skin has a thickness of 1 to 5 mm.